Electrostatic paint spray gun



p 5, 1967 H. w. BEACH, JR 3,339,841

ELECTROSTATIC PAINT SPRAY GUN 5 Sheets-Sheet 1 Filed Feb. 12, 1965 INVENTOR. HOWA/Qp h/ fifflcv/JR. BY

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ELECTROSTATIC PAINT SPRAY GUN Filed Feb. 12, 1965 5 Sheets-Sheet 3 8 INVENTOR.

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ELECTROSTATIC PAINT SPRAY GUN Filed Feb. 12, 1965 5 Sheets-Sheet 4 INVENTOR.

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ELECTROSTATIC PAINT SPRAY GUN Filed Feb. 12, 1965 5 Sheets-Sheet 5 i lz. i i 4.

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/70/4/A/P0 h/ 5:40AM? BY United States Patent 3,339,841 ELECTROSTATIC PAINT SPRAY GUN Howard W. Beach, Jr., 17 Hawthorne Road,

Essex Fells, NJ. 07021 Filed Feb. 12, 1965, Ser. No. 432,301 8 Claims. (Cl. 239-15) This invention relates to an electrostatic paint spray gun, by which is meant one which discharges a spray of paint under pressure and with the paint electrically charged. Some of its features might be applied to paint spray guns in general. The gun may be used to work with liquids other than might be called paint in the technical sense.

An electrostatic paint spray gun must include electrical insulating parts ordinarily made from plastics such as one of the super polyamides, exemplified by nylon or polyethylene or the like. Prior art guns as made commercially include specially molded shapes requiring expensive dies or molds, thus introducing economic problems when the quantity of guns produced is insufficient to justify the die and mold cost. When the production of such guns is suflicient to justify such cost, problems are encountered in connection with the formation in the molded parts of gas bubbles and voids such as plague the molding of plastics in general. In the case of an electrostatic paint spray gun, any discontinuities in any part that should be made of solid plastic presents a hazard because the gmn must be safe when working with electrical charges in the neighborhood of 50,000 volts or more;

One of the objects of the present invention is to provide an electrostatic paint spray gun having plastic parts permitting manufacture of the gun in relatively small quantities at a lower cost than when using specially molded plastic parts, and in doing so to provide a gun having plastic parts free from blow holes, gas bubbles, and the like such as are apt to occur when molding plastic into dies and molds.

An electrostatic paint spray gun must include a very high impedance electrical resistor loaded on or in the gun so that the high impedance end of this resistor is connected as directly as possible to the relatively small paint charging elements of the gun while leaving larger parts which might collect a large electrostatic charge, free from all applied voltage. This is necessary so that if these elements are touched by the operator and current begins to flow, the voltage drops immediately to a safe value, and to free the larger parts such as the necessary handle, control trigger, etc., from collecting a troublesome charge.

In commercial form, resistors suitable for the above purpose are cylindrical and relatively long with terminals at each end. The electrical charging cable is made with a conductor, electrical insulation over this conductor, and metallic shielding over the insulation. This shielding must be grounded electrically so that the gun handle, trigger, etc., are grounded and safe. This introduces the problem that the high voltage can discharge from the cables conductor to its shielding and undesirably reduce the electrical charge on the guns paint charging elements.

Commercially, one practice has been to cut back the electrical shielding from the cable insulation to expose, for example, about six inches of this insulation, and to then connect the cables conductor to the resistor. This provides in such a case a six-inch path which is sufiicient to prevent substantial discharge from the conductor back to the shielding on the cable.

The result of the foregoing is that the gun itself must necessarily at a minimum be long enough to accommodate the six inches of insulation plus the length of the resistor. When the latter is aligned with the cable elements, prior art commercially available guns have been too long to permit their easy manipulation. The cable 3,339,841 Patented Sept. 5, 1967 length free from shielding has been placed in the guns handle with the resistor in the guns barrel, but this requires the angular relation between the cable and resistor corresponding to that of the handle and barrel, and prevents removal and replacement of either or both the cable and the resistor in the field by the gun user.

Another object of the present invention is to provide an electrostatic paint spray gun that is unusually short in length and which provides insulation between the conductors end, which joins with the resistor, and the cable shielding, of adequate length to prevent a discharge from the conductor back to the shielding, while permitting field removal of the resistor and/ or cable by the user.

The gun of the present invention incorporates many other new features of substantial value, as can be understood from the following description.

The electrostatic paint spray gun of the present invention is illustrated by the accompanying drawings in which:

FIG. 1 is a perspective view of the gun;

FIG. 2 is a back view;

FIG. 3 is a front view;

FIG. 4 is a longitudinal section taken on the line 4-4 in FIG. 2;

FIG. 5 is a longitudinal section taken on the line 55 in FIG. 2;

FIG. 6 is a perspective showing a detail of the paint spray hose assembly;

FIG. 7 is a longitudinal section taken on the line 7-7 in FIG. 2;

FIG. 8 shows a portion of FIG. 7 as the parts appear during a different operational phase; I

FIG. 9 is a longitudinal section taken on the line 99 in FIG. 2;

FIG. 10 is a cross section taken on the line 10-10 in FIG. 9;

FIG. 11 is a longitudinal section taken on the line 1111 in FIG. 10;

FIG. 12 is a longitudinal section showing the electrical charging power cable and resistor assembly when re moved from the gun;

FIG. 13 shows a modification of the nozzle end of the gun with some of the parts in longitudinal section;

FIG. 14 is like FIG. 13 except it shows another modification; and

FIG. 15 in an entirely schematic manner shows the gun as it is connected to the necessary electrical power pack and the paint and air supply, and illustrating a special feature which may be used advantageously in connection with the operation of the new gun.

As can be seen from FIG. l in particular, this new gun embodies a body of barrel 1 made of any suitable plastic, such as nylon for example, and which is in the form of a short, stubby length having a cylindrical exterior.

This body 1 is cut to length from a longer piece of standard plastic bar stock. Plastic bar stock is commercially available and, as indicated above, nylon bar is used in this instance. Because it is a simple bar shape, it is inherently free from gas bubble voids, blow holes, or other defects commonly encountered when the same kind of plastic must be heated to a. flowable condition and injected or forced into a die or mold of intricate shape to produce a molding.

The design of the present gun permits the use of such a standard plastic bar which is available to everyone and which, even in small quantity production, permits the cutting one at a time from the longer plastic bar obtained from the plastic manufacturer, into the relatively short lengths required to make the present gun. The reason for the permissible short length is described hereinafter.

As shown by FIG. 4 in particular, this solid plastic bar length cut from the standard bar, is drilled to form a 3 bore 2 which is coaxial with respect to the 'bars cylindrical outside. This bore goes through one end of the bar length and out from the other and it contains the necessary needle valve assembly described hereinafter.

The bore 2 is counterbored at the front end of the barrel 1 to form an enlarged space 3 and from its back or lefthand end the barrel 1 is drilled to form a blind bore 4 which is parallel to the barrels axis but offset therefrom, the barrel or body 1, as shown by FIG. 5, being drilled diagonally from its front end to form a diagonally extending bore 5 which opens into the space 3. This bore 4 is adapted to receivethe paint or other coating liquid which, through the diagonal bore 5, goes to the space 3.

Adjacent to the back end of the barrel 1 the length of plastic bar is transversely drilled to form a relatively large diameter transverse bore 6 adapted to receive a slide or spool valve assembly, described hereinafter, mounted within a length of plastic bar 7. This plastic bar 7 is also a length of plastic bar stock inherently free from defects and which may be purchased by even a low production manufacturer and cut to length and appropriately machined. Its length is shown as being just a little longer than the diameter of the bar forming the barrel 1. The bar 7, as shown by FIG. 7, is drilled coaxially to form a bore including a chamber 8 and the bar 1 is drilled below the bore 4 to form a blind bore 9, seen in FIG. 4, which transverses the smaller diameter bar 7 so as to intersect the lower part of the chamber 8. When air is introduced through the bore 9, it therefore has access to the chamber 8, details of this arrangement being described later.

The bar forming the barrel 1 is further drilled from its front end backwardly and through the smaller bar 7 so as to form bores 10 and 11, shown in FIG. 7, for carrying air from the chamber 8 to the front end of the gun. The bore 10 extends diagonally so that at the front end of the barrel it is located closer to the latters axis than is the bore 11 at that end.

Finally, the bar forming the barrel 1 is drilled to form a dead end bore 12 extending from the back end of the barrel to close to its front end, this bore being for the purpose of receiving the electrical cable and resistor assembly, described later.

It can be seen that the barrel 1 is, in effect, a solid plastic bar free from defects and requiring no molds, dies or the like for its formation. It contains the various passageways required for an electrostatic spray gun in the form of the various bores, without requiring the superimposing of a large number of tubes of special shapes, or special moldings or the like. The plastic is homogeneous throughout, being a plastic bar of initially simple shape in each instance.

To provide the barrel 1 with a handle, an inexpensive sand casting of aluminum, which may be made economically in small quantities, is provided. This metal casting has a handle 13 and a socket member 14 adapted to receive the back end of the barrel 1, the latters back end being unreduced in diameter and the socket of the metal hand piece providing a sliding fit for the barrel. The handle and barrel are held together by three screws 15, which extend through holes formed through the back end of the metal socket 14, as shown by FIG. 2, and into short blind holes drilled in the back end of the bar 1 at locations free from its various bores.

The necessary paint-conducting hose 16 is provided with a standard compression fitting comprising the collar 17, the union 18 and the nut 19, which screws onto the union 18 so as to apply compression to the collar 17. The union 18 itself is screwed through a hole 20 formed in the back end of the hand piece in registration with the bore 4, the latter being counterbored at that end to receive the extending end of the union 18. Thus, the bore 4 may be supplied with paint under pressure, all of the parts required being standard and easily obtainable on the open market or, if necessary, cut to shape in a lathe from standard plastic stock.

Some paints contain solids which tend to clump together. If conductive, they might form an undesirable high conductive electrical path back through the hose 16 to the paint supply tank. Therefore, the hose 16 is shown as containing a smaller hose 16a which extends up nearly to the front of the bore 4, the end of the union 18 terminating close to the back end of the barrel 1. Therefore, the paint under pressure introduced to the bore 4 and not required for use by the gun, can go back through the pipe 16a and down the hose 16 back to the paint supply where, by means of a suitable pressure pump (not shown) it can be re-introduced to the paint supply. Such recirculation would occur constantly during the use of the gun and provides an advantage when the paint includes paint particles, which might even be metallic, from clumping solidly. This feature of recirculation is not required at all times.

At the front or right-hand end of the barrel 1, the bore 2 is counterbored and threaded to receive a metal bushing 21 into which is screwed a metal fluid tip 22 having a central hole 23 through which the paint is to be ejected. This is under the control of a needle valve 24 which, when moved forwardly and backwardly relative to the hole 23, controls the amount of paint ejected. When the paint itself is electrically charged with high voltage, by means explained later, this fluid tip 22 and the needle valve 24 become correspondingly charged, the latter, therefore, being provided with a forwardly extending needle 25 to assist in the electrostatic action on the discharge paint spray. The needle valve 24 is controlled by a stem assembly 26 which goes backwardly through the bore 2, the forward end of this stem being connected to the needle valve arrangement, and its back end sliding in a supporting bushing 27 screwed into a counterbore formed in the back end of the bore 2. The stem is provided with a collar 28, and a compression spring 29 normally urges the stem 26 forwardly so as to move the needle valve 24 forwardly to its closing position relative to the hole 23.

Control of the above valve stem assembly 26 is effected by a trigger bar 30 pivoted at its upper end to the socket 14 and which extends from there downwardly through a saddle 21, which is part of the assembly, and on to below the barrel where a trigger 32 is fixed to the bottom end of the bar 30. To provide for the passage of the bar 30 through the bar 1, the latter has a transverse passageway 33 machined therethrough as required for this purpose. The lower part of this passage 33 bisects the dead end bore 9, previously described, at a location below the bore 2. The stem assembly 26, as shown by FIG. 4, is in effect two sections interjoined by the saddle 31 and when the trigger 32 is pulled, the stern assembly 26 is pulled backwardly against the compression of the spring 29 and the needle valve 24 is pulled backwardly to its open positron more or less depending upon the displacement of the trigger 32.

The front end portion of the valve stem 26 is guided by a bushing 34 screwed into a counterbore formed in the bore 2 inside of the counterbore in which the bushing 21 and fluid tip 22 are installed. An O-ring 35 seals this bushing within the counterbore against the leakage of paint backwardly, which, of course, may be charged with high voltage. This is a static seal and, therefore, works satisfactorily. However, since the stem 26 must slide through the bushmg 34 a seal must be provided somehow to prevent the loss of paint between the bushing 34 and the forward stern portion of the stem assembly 26. This requires a dynamic seal because of the sliding motion and the provision of a completely fluid-tight seal presents a serious problem.

In the present gun, the above problem has been solved by the use of cylindrical Teflon rod stock which is machined out to form a Teflon bellows 36 which is integral with the bushing 34 and to form integrally a mount 37 which connects with the needle valve 24 and to the stem 26. These parts 34, 36 and 37 are one part, free from joints of any kind. This arrangement eliminates the need for a dynamic sliding seal such as might be provided by an O-ring and which, under the conditions of service to which this gun is subjected, is unsatisfactory. The Teflon bellows collapses and expands as required for movement of the stem 26 while presenting a solid wall of Teflon machined from the Teflon rod which, incidentally, is commercially available to anyone. Being machined from solid rod stock, this bellows and the parts 34 and 37 are free from all discontinuities and resist satisfactorily the damaging etfects of all known paints or other coating liquids even when they are under the high electrostatic charge required for electrostatic spray painting.

The bushing 34, the bellows 36 and the needle valve mount 37 are formed from electrically insulating plastic so that the stem 26 is completely shielded from the charged paint. The stem 26 is itself made from plastic, to prevent arcing between the electrostatically charged paint and this stem part. The described construction completely prevents the leakage of the electrically charged paint back to the metal parts which are grounded.

At its front end, the barrel bar 1 is machined to form a reduced portion having external threads 38 and its front end face is machined to form two circular grooves 39 and 40. The front end of the bore connects with the groove 39 and the front end of the bore 11 connects with the groove 40.

A fan spray nozzle 41 is machined, again from solid plastic bar stock, to form a centrally located opening through which the discharge end of the fluid tip projects while leaving an annular space therearound. The opening is enlarged as required to give clearance for the main body of this tip 22, and as required so that at the inside face of the nozzle, when this face abuts the front end of the barrel 1, this space 42 registers partially with the groove 39. Thus, compressed air introduced to the groove 39 by the bore 10 goes through the annular space around the fluid tipss discharge end and provides for atomizing paint or other liquid ejected through this tip when the trigger 32 is pulled.

The groove 39 may be eliminated if desired, because the outlet of the diagonal bore 10 registers with the space 42 in the back of the nozzle. The annular space around the fluid tip provides a back pressure so the compressed air in the space 42 builds up to give a more even and uniform paint atomizing discharge of air. This effect of choking back the air is also provided by the partial registration of the space 42 with the groove 39 when it is used.

The back end face of the nozzle 41 is machined to provide an annular groove 43 which registers partially with the groove 40 in the abutting end of the barrel 1, and the nozzle, being machined to form wing tips, is further drilled as required to form paint fan spray forming ducts 44. Excepting that the nozzle 41 is machined-from the plastic bar, the shape of this nozzle may be more or less conventional. It is retained in abutting relation with the end of the barrel by means of a coupling collar 45, which engages the nozzle and is screwed on the threads 38 of the reduced end portion of the barrel. The outside diameter of this coupling collar 45 is made the same as the outside diameter of the barrel, this coupling collar, in fact, being machined from the same diameter of plastic bar as that from which the barrel is made. All of these parts are plastic and can be machined to shape on an ordinary lathe in connection with small volume production of the gun.

The partial registration of the grooves 40 and 43 provide a choking effect building up a back pressure for the fan spray air. In all instances this back pressure serves to prevent excess air flow in line with the hole of the bore through which the air is introduced to the nozzle elements.

The bore 9, previously described, is provided with a coupling 46 for an air hose 47 through which compressed 6 air may be introduced to the bore 9 from where it goes into the recess 8 formed in the short cross bar 7. Control of this air is provided by a valve assembly located in the counterbore drilled in the outer end of the bore 9.

The above assembly, as shown by FIG. 4, includes a valve seat 48 located in this counterbore and a conical valve head 49 biased to its closed position by a compression spring 50. This valve may be pushed open by an operator 51 engaged by the lower end portion of the trigger bar 30 when the trigger 32 is pulled, this operator being sealed by an O-ring 52 to prevent leakage of the air outwardly through the slot 33 cut to provide room for the trigger bar 30. The arrangement is such that when the trigger is pulled the air valve 49 is opened before the paint control needle valve 24 is pulled open, in accordance with ordinary paint gun practice.

When the valve 49 is opened, compressed air has access to the chamber 8. The bar 7, as shown by FIG. 7, is suitably counterbored to mount a slide or spool valve assembly comprising a push button 53 having a conical inner valve head end 54 which can close the chamber 8 from the bore 11 when pushed to the right. This push button 53 is screwed on to a threaded bar screw 55 which connects with a spool valve head 56 which slides in a sleeve 57 having ports 58. This valve head 56 is carried by another push button 59. When the push button 53 is pushed to the right, as shown in FIG. 8, the valve 54 closes off the air through the bore 11 which feeds compressed air ultimately to the fan jet openings of the nozzle, while moving the spool valve head 56 to the right so as to open the port 58 more or less depending on the longitudinal adjustment of the sleeve 57, and by the adjustment possible through the screw 55. This sleeve 57 is made longitudinally adjustable by being screwed into a bushing 60 screwed into the righthand end of the bore forming the central chamber 8, this bore being counterbored for this purpose and appropriately threaded. The sleeve valve has a projecting end 61 which is externally accessible as shown by FIG. 2. By turning this end 61, the sleeve valve may be moved inwardly and outwardly.

In addition, as previously noted, the bar 55 interconnecting the two push button members is screw threaded into each of the push buttons and each of the latter has a knurled outer end so that it may be turned. In this Way the spacing between the valve portions of the two push button assemblies may be varied to control respectively the air passed through the bores 10 and 11, which in turn depends upon which push button is pushed. Suitable 0- rings 62 prevent leakage around the push buttons out- Zvardly through the ends of the bore formed through the In operation, to obtain a fan spray the righthand push button 59 is pushed in completely closing the ports 58 and opening the valve head 54, as shown by FIG. 7. When a cone spray is desired the push button 53 is pushed in, as shown by FIG. 8.

At all times some air is passed through the bore 10 whenever the trigger is pulled, this being because the counterbore in which the valve sleeve 57 is fitted is of a somewhat greater diameter than the outside valve sleeve diameter. The amount of air thus continuously passed is adjustable by rotation of the end 61. This arrangement is to assure proper atomization of the paint when the push button 59 is pushed in so as to close off the ports 58 completely. Ordinarily, adjustment of this air need not be made 'by the gun operator, it being suflicient to turn the end 61 so as to obtain proper atomization at all times and to then rely on rotation of the push button 59 or 53 to control the amount used for the cone spray.

An important feature of this new gun is the manner in which the cable from the necessary power pack is devised. This is shown in detail by FIG. 12. The cable itself has the external metallic shielding 63. This overlaps a metal fixture or terminal 64 which fits in an appropriately drilled hole in the back end of the socket or hand piece 14, where this fixture is retained by a removable retainer plate 65 held in position by removable screws 66 screwed into the back end of the hand piece and which overlaps the portion or flange 64. Ordinarily, the high voltage cable and resistor assembly of a gun of this type can not be made removable and it is necessary to return the entire gun to the manufacturer when cable or resistor replacement is required for any reason.

In the present instance, the shielding 63 is cut back from the cable insulation 67 only a short distance and a short length of the inner electrical conductor 68, which carries the high voltage of 50,000 volts or more, is exposed.

Ordinarily the insulation 67 is polyethylene, although other plastics might be used. In any event, tubular plastic stock of corresponding composition and density is cut to form a sleeve 69. This stock has an inside diameter forming a forced friction fit with the outside of the insulation 67.

If the latter is polyethylene of a given density, the sleeve 69 is made of polyethylene of corresponding density. With the sleeve 69 applied by a force fit over the insulation 67, the sleeve 69 is rotated at high speed so as to fusion weld its inside to the outside of the insulation 67. The two become integrally joined as one.

Now, although short, the sleeve 69 is made long enough to receive the necessary high impedance electrical resistor 70 which is pushed inside this sleeve with its inner terminal 71 connected to the exposed conductor 68. This resistor may be simply slid into position but it ordinarily fits tight enough to be frictionally retained against falling out.

With the above construction, the electrical discharge path from the exposed conductor 68 to the grounded shielding 63 is about double the actual length of the sleeve 69. This path is from the conductor to the front end of the sleeve and then back to the grounded shielding; for example, the sleeve may be only about four inches long. One inch, for example, would be on the insulation 67 and integrally joined therewith by the spin fusion process. Thus the discharge path becomes about three inches to the sleeves free end, and about four inches back outside of the sleeve to the shielding. These are approximate values, but it can be seen that the discharge path can be made substantially longer than the six inches considered adequate commercially. The prior art arrangement requires the six-inch cable length with the shielding removed from the conductors insulation plus the length of the resistor.

Furthermore, if this new high voltage cable assembly is removed from the gun, by removing the retainer 65, with the power pack connected and in operation, and should the resistor 70 inadvertently fall from the sleeve 69, the space between the conductor 68 and the end of the sleeve can be made sufficiently long to prevent a serious spark from jumping from the conductor 68 to the end of the sleeve and, therefore, possibly to whoever has disconnected the assembly. Assuming that the resistor 70 stays in position, its opposite or free end terminal can impart no discomfort because the moment any current flows the resistor drops the voltage radically, due to its very high impedance.

As shown by FIG. 9, the front end of the barrel 1 is drilled diagonally to form a hole intercepting the bottom of the bore 12 and a conductor 72 extends through this hole from the metal bushing 39 to a metal plate 73 located in the bottom of the bore 12. A compression spring 74 is located on this plate 73 so as to press the resistor 70 back towards the conductor 68. In this way the high voltage is carried from the resistors front or high impedance terminal directly to the bushing 39, and so to the fluid tip 22 whereby to charge the discharged paint or other liquid.

A neon glow lamp or its equivalent 75 is positioned between the resistors outer terminal end 76 and the plate 73. When the power pack is on and the gun is, therefore, charged, this glow lamp glows. If the nylon bar from which the barrel is made is of the translucent variety, the glow can be seen from the outside of the gun and warns the operator that the gun is charged. If better visibility is desired, or if an opaque plastic is used for the barrel, a hole may be drilled transversely through the barrel to the lamp and a lucite rod 77 positioned in this hole, as shown particularly well by FIGS. 10 and 11. The projecting end of this rod may be cut so that light from the glow lamp transmitted through this rod may be seen directly by the gun operator who is, of course, behind the gun.

The cable shielding 63 is in electrical contact with the metal hand piece 14 and goes back to the power pack which is itself grounded. Therefore, the hand piece 14 and its associated metal parts are kept at ground potential at all times. This means that, like the work being coated which is also kept at ground potential, there is sometimes a tendency for the ejected electrostatically charged paint spray to be attracted to the outside of the barrel 1 and to the operator of the gun.

To prevent the above trouble, in FIG. 1 the barrel 1 is encircled by a metal wire ring 78 and, as shown by FIG. 4, this ring connects with an electrical connector 79 extending inwardly through the barrel by way of a suitably drilled hole to the chamber 3, a metal sleeve 80 located in the counterbore there serving to connect this element 79 with the bushing 39 which, as previously indicated, is connected to the front terminal of the resistor 70 and, therefore, is charged at the full gun potential as it exists during the normal operation of the gun. With this ring 78 at the same potential as the paint, for all practical purposes, the latter is repelled against its described possible tendency to coat the outside of the gun and the operator of the gun.

A modification of the above arrangement is shown by FIG. 13 wherein the ring 78a is located around the plastic nozzle 41 and connects with the fluid nose piece 22 by way of a conductor 79a.

In the second modification shown by FIG. 14, there is essentially the same arrangement excepting that instead of the ring 78a, shown in FIG. 13 as a round wire ring, a flanged annular metal piece 78b is used.

It can be seen that in the normal operation of the gun complete safety is insured. All plastic parts are made of rod or tube shapes which may be obtained from any plastic manufacturer in a completely homogeneous condition. The plastic forming process for rod, bar, tube, etc., assures this condition inherently. Because of the resistor 70, assuming it to have the proper impedance value, the fluid tip- 22 or the needle 25 may be touched without fear of lethal shock. This applies also to the paint guard rings 78, etc., shown in the drawings. Leakage of the charged paint can not possibly occur backwardly because of the need for moving the needle valve operating stem 26 because of the Teflon bellows seal. If the gun operator removes the high voltage cable he can not be injured regardless of his carelessness. This is true even if the resistor 70 is removed from the sleeve 69. The operator can not possibly remove the sleeve 69 because it is an integral part of the cables insulation 67. The length of the sleeve 69 may be made sufficient to avoid an are discharge from the conductor.

Referring now to FIG. 15, a compressed air line 81 feeds the guns air line 47 and applies pressure to a paint reservoir 82, so that the paint is force-fed to the guns tube 16. Both the tubes 16 and 47 are made of a flexible plastic and are electrically non-conducting. The paint reservoir 82 is isolated from ground by electrical insulators 83. This arrangement has the advantage that no voltage is lost through the charged paint because the paint supply is isolated from ground.

The above described electrical isolation from ground is not effective if the metal handle 13 is not also isolated from the charged paint, because of grounding through the cable shielding 63 and grounded power pack. This is 'why the union 18 is shown in FIG. as being made of plastic, a sealing gasket 18a and ring 1812 preventing backward leakage of the paint. For obvious reasons any other parts within sparking distance from the charged paint and having adequate electrical capacity to become charged by the charge on the paint should be made of plastic or other non-conducting material.

What may be a conventional power pack 84, provides the high voltage. Its output on one side goes to ground at 85 and the high voltage goes through the cable previously described and in the schematic drawing is numbered 63. Interposed in the conductor this cable is a suitable microampere relay 86. As schematically shown, this includes an indicator pointer arranged so that when this swings to indi-. cate a pre-determined rnicroampere value, it closes contact with an electrical contactor 87. When this occurs, through a circuit indicated at 88, powered by a battery 89, a relay 90 is operated. This relay is in circuit with the power fed to the power pack to operate it, and when the relay opens the power pack is deactivated. Although not indicated, a relay could be used to ground out its high voltage side simultaneously.

With the above arrangement, assuming that the contactor 87 is set adjustably and appropriately, when the gun is brought too close to a grounded object, the power pack 84 is deactivated so as to terminate the high voltage charge on the gun. Deactivation may be adjusted to occur at various distances of the gun from the grounded object. Using a commercially available microammeter relay system, to apply the above principle, experiments have shown that the guns charge may be cut off at varying distances from the grounded object ranging from less than an inch upwardly to some eight inches. Thus, protection is provided against even a very careless hand gun operator. If this principle is applied to an automatic gun, it provides protection in the case of conveyed objects that are improperly oriented so they pass too close to the gun. This arrangement terminates any arcing that might occur under any circumstances.

The compactness and good balance of the new short gun may be appreciated particularly well from looking at FIG. 1. The heavy weight of the short, stubby barrel is balanced by the weight of the necessary high voltage cable and the air and paint supply hoses. The short length would be impossible with the prior art arrangements.

Features not described specifically hereinabove do not require much discussion since their function should be obvious. For example, the arrangement shown at 91 is only to provide the trigger with an adjustable displacement limit to control the opening of the needle valve and, therefore, the flow of paint.

However, before closing, attention is again called to the fact that because of the unique cable and resistor assembly, this entire assembly fits the short length of the stubby gun barrel. No part need be in the handle, and because the cable end and resistor are aligned the assembly can be slid in and out of the gun by the operator in the field, somewhat like a breech loading pistol.

What is claimed is:

1. An electrostatic paint spray gun including an electrically non-conductive barrel having a central longitudinal passage, electrostatic paint spray means on the front of said barrel adapted to be charged with high voltage electric current, means for supplying paint to the front portion of said passage, the latter communicating with said spray means, a valve adjacent to said spray means for controlling the flow of paint from the front portion of said passage to this spray means, a movable valve actuating rod extending from said valve backwardly through said passage to a location where the rod may be controlled, sealing means spaced backwardly from said passages front portion and forwardly from said location for preventing the backward flow of paint through said passage, at least the portion of said rod exposed to the paint in said passage between said sealing means and said spray means being electrically nonconductive so that paint supplied to said passages front portion is electrically isolated from the balance of this rod; wherein the improvement comprises said barrel being made of solid electrically non-conductive material with said central passage formed therein, said paint supply means including a passage formed through said barrel laterally offset from said central passage from therback end of said barrel forwardly and terminated adjacent to the front portion of this barrel and connecting therewith by a branch passage extending from this front portion to the adjacent portion of this offset passage.

2. The gun of claim 1 in which the improvement further comprises'forming said paint and branch passages through said solid material with said passages bounded completely without interruptions by the solid material.

3. The gun of claim 1 in which the improvement further comprises said sealing means being formed by a flexible annulus connected immovably to the inside of said central passage and to said rod.

4. The gun of claim 1 in which an electrically conductive member is on the back end portion of said barrel at least adjacent to the opening of said laterally oifset passage, the latter having an electrically non-conductive tubular extension projecting fluid-tightly beyond said opening and conductive member for connection to a supply of paint.

5. The gun ofclaim 4 in which a second passage is formed and which extends forwardly from the back end of said solid barrel material through the barrel laterally off set from both said central passage and first-named laterally offset passage and is terminated adjacent to this barrels front portion and having a branch extension extending from said electrostatic spray means to the adjacent portion of this second passages extension, and means for electrostatically charging said spray means including a high impedance high voltage electrical resistor inserted longitudinally in said second oifset passage with the front end of this resistor adjacent to and releasably connected with said spray means by a conductor in the forward end of this passage and in this passages branch passage, a high voltage electric cable having a conductor covered by electrical insulation with the latter covered by electrically conductive shielding which is grounded, said cable having an end portion with said shielding terminating and electrically connected to said electrically conductive member on the end of said barrel and with said insulation extending from the shielding termination into said second offset passage and with said conductor forming an electrical connection with the back end of said resistor to conduct high voltage current thereto, said connection forming an electrical discharge path between it and the termination of said grounded shielding and which must be long enough to avoid material current flow thereover, an electrically nonconductive sleeve fitted over said cables insulation extending from said shielding termination with this sleeve integrally joined with this insulation and extending integrally over said connection and said resistor for substantially the length of the latter and interposed between it and the inside of said second laterally offset passage and slidably removable from the latter, whereby said electrical discharge path is substantially double the length of said resistor and said resistor and sleeve may be removed for servicing.

6. An electrostatic paint spray gun including an electrically non-conductive barrel, means in the front end portion of said barrel for forming an electrostatically charged paint spray, an electrically conductive element on the outside of said barrel and spaced backwardly from said spray forming means, means for supplying said spray forming means with paint, a high impedance electrical resistor mounted longitudinally by said barrel with the front end of this resistor electrically connected with said spray forming means, a high voltage electric cable having a conductor covered by electrical insulation which is covered by electrically conductive shielding which is grounded, said cable having an end portion with said shielding terminating and electrically connected to said element on the outside of said barrel and with said insulation extending therefrom and with said conductor forming an electrical connection with the back end of said resistor to conduct high voltage current thereto, said connection forming an electrical discharge path between it and the termination of said grounded shielding and which must be long enough to avoid material current flow thereover; wherein the improvement comprises an electrically non-conductive sleeve fitted over said cables insulation extending from said shielding with this sleeve integrally joined with this insulation and extending integrally over said connection and said resistor for substantially the length of the latter, whereby said electrical discharge path is substantially double the length of said resistor and the portion of said insulation extending from the termination of said shielding may be made generally correspondingly shorter.

7. A hand-held electrostatic paint spray gun having a barrel that is short as compared to its diameter, an electrostatic paint spray nozzle on the front of said gun and which must be charged with high-voltage current, a metal handle mounting said barrel by its back end, a high-voltage cable having electrical insulation and an electrical insulation sleeve extending forwardly therefrom and integral therewith, a high-voltage high-impedance resistor inserted within said sleeve, said cable having a conductor, an electrical connection between the end of said conductor and the back end of said resistor, said barrel having a hole opening from its back end and extending longitudinally through this barrel to a location adjacent to the latters front end and said sleeve and resistor being inserted slidably in said hole, said cable having an electrically conductive grounded shielding removably connected to the back end of said barrel and electrically connected with said handle, said cable and sleeve and resistor being removable from the back end of said barrel and the electrical discharge path from said electrical connection of said conductor and resistor being from said connection forwardly to the front end of said sleeve and doubling back to said shielding, and means for connecting the front end of said resistor electrically to said nozzle when said resistor and sleeve are inserted in said hole.

8. The gun of claim 7 in which said barrel has a second hole opening from its back end and laterally displaced from the first-named hole, said barrel having solid integral electrically non-conductive material through which said second hole is formed to lead to said nozzle, and an electrically non-conductive conduit means extending backwardly from said second holes opening until free from said metal handle and constructed for connection with an electrically non-conductive hose for supplying paint, whereby the paint is isolated from said handle which is electrically connected to said grounded shielding.

References Cited UNITED STATES PATENTS 3,042,312 7/1962 Packard 239586 3,169,882 2/1965 Juvinall et al 239-15 3,233,831 2/1966 Fraser 23915 3,235,186 2/1966 Boyce 239297 EVERETT W. KIRBY, Primary Examiner.

M. HENSON WOOD, JR., Examiner.

R. S. STROBEL, Assistant Examiner. 

1. AN ELECTROSTATIC PAINT SPRAY GUN INCLUDING AN ELECTRICALLY NON-CONDUCTIVE BARREL HAVING A CENTRAL LONGITUDINAL PASSAGE, ELECTROSTATIC PAINT SPRAY MEANS ON THE FRONT OF SAID BARREL ADAPTED TO BE CHARGED WITH HIGH VOLTAGE ELECTRIC CURRENT, MEANS FOR SUPPLYING PAINT TO THE FRONT PORTION OF SAID PASSAGE, THE LATTER COMMUNICATING WITH SAID SPRAY MEANS, A VALVE ADJACENT TO SAID SPARY MEANS FOR CONTROLLING THE FLOW OF PAINT FROM THE FRONT PORTION OF SAID PASSAGE TO THIS SPRAY MEANS, A MOVABLE VALVE ACTUATING ROD EXTENDING FROM SAID VALVE BACKWARDLY THROUGH SAID PASSAGE TO A LOCATION WHERE THE ROD MAY BE CONTROLLED, SEALING MEANS SPACED BACKWARDLY FROM SAID PASSAGE''S FRONT PORTION AND FORWARDLY FROM SAID LOCATION FOR PREVENTING THE BACKWARD FLOW OF PAINT THROUGH SAID PASSAGE, AT LEAST THE PORTION OF SAID ROD EXPOSED TO THE PAINT IN SAID PASSAGE BETWEEN SAID SEALING MEANS AND SAID SPRAY MEANS BEING ELECTRICALLY NONCONDUCTIVE SO THAT PAINT SUPPLIED TO SAID PASSAGE''S FRONT PORTION IS ELECTRICALLY ISOLATED FROM THE BALANCE OF THIS ROD; WHEREIN THE IMPROVEMENT COMPRISES SAID BARREL BEING MADE OF SOLID ELECTRICALLY NON-CONDUCTIVE MATERIAL WITH SAID CENTRAL PASSAGE FORMED THEREIN, SAID PAINT SUPPLY MEANS INCLUDING A PASSAGE FORMED THROUGH SAID BARREL LATERALLY OFFSET FROM SAID CENTRAL PASSAGE FROM THE BACK END OF SAID BARREL FORWARDLY AND TERMINATED ADJACENT TO THE FRONT PORTION OF THIS BARREL AND CONNECTING THEREWITH BY A BRANCH PASSAGE EXTENDING FROM THIS FRONT PORTION TO THE ADJACENT PORTION OF THIS OFFSET PASSAGE. 